1. Field of the Invention
The present invention relates to a relief device for an oil pump that can ensure an appropriate pressure of oil discharged from the oil pump in a high-revolution region of an engine, ensure good lubrication ability in a medium-revolution region, and improve the efficiency of the engine.
2. Description of the Related Art
A relief valve is often installed, downstream of an oil pump, as a device for preventing an excessive increase in the discharge pressure of the oil pump. The conventional relief valves have a function of protecting the flow channel and devices located thereon from an extremely high oil pressure, but in recent years the emphasis has been placed on reduction of ineffective operations of the oil pump by the adjustment of oil pressure to the intended value in order to reduce fuel consumption.
The relief valves as means for adjusting the discharge pressure of oil pumps in order to realize the abovementioned function have been actively researched and developed. Thus, Japanese Patent Application Publication No. H10-318158 discloses the configuration of a relief valve as means for adjusting the discharge pressure of an oil pump in which ineffective operations of the oil pump are reduced by ensuring the relief (discharge) of oil in a medium-revolution region of the engine.
In Japanese Patent Application Publication No. H10-318158, a control valve 30 is configured by a valve housing 31 having an inner hole 31a and also a control port 31b, a sub-port 31c, and a main port 31d that communicate with the inner hole 31a; a spool 32 that is installed to be axially slidable in the inner hole 31a of the valve housing 31, receives at one end thereof the pressure of work oil flowing in through the control port 31b, forms, together with the valve housing 31, variable throttle portions A and B, and performs variable control of connecting and disconnecting the ports 31b, 31c, and 31d by a land portion 32a; and a spring 33 that biases the spool 32.
The control port 31b communicates with a discharge port 21e, the sub-port 31c communicates with a sub-intake port 21d, and the main port 31d communicates with a main intake port 21c. The land portion 32a of the spool 32 is formed integrally therewith at one end side of the spool 32, and a slope face 32b that is inclined from the outer circumferential portion of the land portion 32a toward the axial center of the spool 32 is formed at the other end side of the land portion 32a. A diametrical step 32c is formed between the end portion of the slope face 32b on the land portion 32a side and the outer circumference of the land portion 32a. 
Specific features of the control are mainly manifested in the second control mode and third control mode. In the second control mode, the sub-port 31c and the control port 31b communicate via the variable throttle portion A in a state in which the communication of the sub-port 31c and the main port 31d is maintained, and the work oil flows from the main port 31d and the control port 31b into the sub-port 31c. In the third control mode, the sub-port 31c and the main port 31d communicate via the variable throttle portion B in a state in which the communication of the sub-port 31c and the control port 31b is maintained, and the work oil flows from the control port 31b into the sub-port 31c and the main port 31d.
In order to perform the above-described control, the axial dimension L of the land portion 32a is made less than the axial dimension of the sub-port 31c. As a result, when the land portion 32a is positioned right beside the sub-port 31c, gaps appear at both (upper and lower) axial ends of the land portion 32a and the work oil can communicate with the flank of the land portion 32a (see Japanese Patent Application Publication No. H10-318158, FIGS. 7 and 8).
The following problems are associated with Japanese Patent Application Publication No. H10-318158 in which the abovementioned configuration and control are disclosed. Thus, the high-revolution region of the engine (oil pump 20) corresponds to the fifth control mode and FIG. 10 in Japanese Patent Application Publication No. H10-318158. Thus, in the high-revolution region of the engine, the work oil flows from the control port 31b (discharge port 21e) into both the sub-port 31c (sub-intake port 21d ) and the main port 31d (main intake port 21c ). The resultant problem is that in the high-revolution region of the engine, the oil pressure unexpectedly becomes too low.
In the configuration disclosed in Japanese Patent Application Publication No. H10-318158, when the revolution speed N of a crankshaft 10 is equal to or greater than N1 (characteristic of point (a)), the sub-port 31c is open at all times. In other words, from a revolution region slightly higher than the idling revolution region to a maximum (MAX) revolution region, minimum one location is open.
Therefore, since the aforementioned sub-port 31c is open at all times in the configuration disclosed in Japanese Patent Application Publication No. H10-318158, it is structurally impossible for the configuration to perform a control, for example, such that temporarily closes the control valve 30 to ensure lubrication in the medium-revolution region of the engine and opens the control valve 30 again to improve the efficiency in the high-revolution region of the engine. It is an object of the present invention (technical problem to be resolved by the present invention) to ensure an appropriate pressure of oil discharged from the oil pump in a high-revolution region of the engine, ensure good lubrication ability in a medium-revolution region, and improve the efficiency of the engine.
The inventors have conducted a comprehensive study aimed at the resolution of the above-described problems and have found that those problems can be resolved by the first aspect of the present invention residing in a relief device for an oil pump, including a relief housing constituted by a relief inflow portion, a valve passage portion, a recess, and an oil discharge portion having a relief hole; a relief valve having a small-diameter portion between a first large-diameter portion and a second large-diameter portion; and a spring elastically biasing the relief valve toward the relief inflow portion, wherein the recess is formed at a position that is closer to the relief inflow portion side than to the oil discharge portion, the axial length of the recess is larger than the axial length of the first large-diameter portion of the relief valve, and the shortest axial distance between the recess and the relief hole is less than the axial length of the small-diameter portion.
The aforementioned problems are also resolved by the second aspect of the present invention which is the first aspect, wherein the recess is formed by a main recess that is formed at a front side of the valve passage portion and an auxiliary recess that is formed on an opposite side to the main recess, with the valve passage portion being interposed between the auxiliary recess and the main recess, and the main recess and the auxiliary recess are formed linearly. The aforementioned problems are also resolved by the third aspect of the present invention which is the first or second aspect, wherein the recess is formed as a narrow hole extending in the axial direction. The aforementioned problems are also resolved by the fourth aspect of the present invention which is the first aspect, wherein the widthwise dimension of the recess is less than a diameter of the valve passage portion.